Several geo-political factors have recently made the synthesis of bio-fuels an attractive alternative to conventional sources of crude oil. For example, political unrest in many countries supplying oil has resulted in unanticipated interruptions in oil shipments. Additionally, global warming caused by increasing atmospheric CO2 levels which in turn is caused by burning fossil fuels with no corresponding re-absorption of the CO2 is beginning to profoundly affect the atmosphere. Thirdly, the supply of oil has reached a tipping point where demand now exceeds supply, and the price of oil is expected to continue to rise until the supply of oil is exhausted. Nonetheless, the world's economies cannot quickly change from fuels based on oil to other sources of energy, so oil is expected to remain in high demand for at least the next few decades.
All of these factors have motivated the search for alternate sources of oil, particularly sources based on green technologies in which the synthesis of the oil uses CO2 from the atmosphere or otherwise sequestered from industrial processes or the combustion of fossil fuels.
One green oil-producing technology utilizes algae from which lipids and other organic molecules can be harvested and used as feedstock for reactors in which bio-fuels (e.g., diesel fuel) are produced. The key to the successful implementation of this technology is that the algae growth process must be low-cost and efficient, whereby the raw materials for accelerated algae production—nutrients, CO2, and light—are applied to the photobioreactor in the right quantities and at the right time. Further, since algae is a living organism, the growth environment must preclude the presence of competing organisms and organisms and materials that can otherwise hinder the accelerated growth of the algae.
Recent developments in this area include the article by Gordon, et al, Ultrahigh Bioproductivity from Algae, Appl Microbiol Biotechnol 76:969-975 (2007), which is herein incorporated by reference in its entirety, which discloses how low duty factor high peak irradiance illuminating light can greatly accelerate algae growth. However, an efficient mechanism of generating the prescribed illumination has not been presented. Further, there is no discussion or suggestion of an efficient and effective mechanism for generating the prescribed illumination from solar radiation.
Other developments in this area include a, “Method for Improved Plant Growth” disclosed in U.S. Pat. No. 5,209,012 to Palmer, which is herein incorporated by reference in its entirety, and discloses lighting cycled on and off for predetermined periods for plant growth. To illustrate these developments, an example of a prior art light delivery system for a bioreactor is illustrated in FIG. 1. This prior art light delivery system has a photovoltaic panel 90 that collects solar radiation and coverts it to electrical power and a DC generator 92 that generates electrical power during those times the sun is not available. Batteries 91 are used to store the electrical power produced by the photovoltaic panel 90 or the DC generator 92. This prior art light delivery system also includes a connection to the local A/C power source 94 which provides alternating current electrical power to an AC-to-DC converter 93 whose output is connected to direct current bus 95. The direct current bus 95 routes the DC electrical power to the broadband lights 96. The output of the batteries 91 and DC generator 92 also can be connected to and provide electrical power to the direct current bus 95.
In an exemplary operation of the prior art light delivery system for the bioreactor shown in FIG. 1, electrical power originating at the photovoltaic panel 90, the batteries 91, the DC generator 92, or the local A/C power source 94 (through AC-to-DC converter 93) is routed to the broadband light 96 through the direct current bus 95. The broadband lights 96 illuminate the photobioreactor 98 with light 97 that is continuous and without modulation, which has been shown in the prior art to be sub-optimal. Additionally, most botanical organisms are sensitive to only one or two relatively narrow wavelength bands of illuminating light and as a result the broadband illumination produced by the broadband lights 96 in this prior system is inefficient and wasteful.